TST: simple ties test for hierarchical clusterers

scipy/cluster/tests/test_hierarchy.py

@@ -97,6 +97,35 @@ def check_linkage_q(self, method):
         assert_allclose(Z, expectedZ, atol=1e-06)
 
 
+class TestLinkageTies(object):
+    _expectations = {
+        'single': np.array([[0, 1, 1.41421356, 2],
+                            [2, 3, 1.41421356, 3]]),
+        'complete': np.array([[0, 1, 1.41421356, 2],
+                              [2, 3, 2.82842712, 3]]),
+        'average': np.array([[0, 1, 1.41421356, 2],
+                             [2, 3, 2.12132034, 3]]),
+        'weighted': np.array([[0, 1, 1.41421356, 2],
+                              [2, 3, 2.12132034, 3]]),
+        'centroid': np.array([[0, 1, 1.41421356, 2],
+                              [2, 3, 2.12132034, 3]]),
+        'median': np.array([[0, 1, 1.41421356, 2],
+                            [2, 3, 2.12132034, 3]]),
+        'ward': np.array([[0, 1, 1.41421356, 2],
+                          [2, 3, 2.44948974, 3]]),
+    }
+
+    def test_linkage_ties(self):
+        for method in ['single', 'complete', 'average', 'weighted', 'centroid', 'median', 'ward']:
+            yield self.check_linkage_ties, method
+
+    def check_linkage_ties(self, method):
+        X = np.array([[-1, -1], [0, 0], [1, 1]])
+        Z = linkage(X, method=method)
+        expectedZ = self._expectations[method]
+        assert_allclose(Z, expectedZ, atol=1e-06)
+
+
 class TestInconsistent(object):
     def test_inconsistent_tdist(self):
         for depth in hierarchy_test_data.inconsistent_ytdist: